docs($parse): fix typo in error message description

Closes #13409

src/ng/parse.js

@@ -1069,7 +1069,7 @@ ASTCompiler.prototype = {
       right = this.nextId();
       left = {};
       if (!isAssignable(ast.left)) {
-        throw $parseMinErr('lval', 'Trying to assing a value to a non l-value');
+        throw $parseMinErr('lval', 'Trying to assign a value to a non l-value');
       }
       this.recurse(ast.left, undefined, left, function() {
         self.if_(self.notNull(left.context), function() {